1. Field of the Invention
The present invention relates to a fuel injector. Specifically, the present invention relates to a technique for reducing the diameter of a fuel injector.
2. Background of the Invention
FIG. 8 shows a longitudinal section of a conventional fuel injector 100. The fuel injector 100 comprises a valve body 116, a core 122, a valve seat 112, a valve 110, a spring 120, and a solenoid coil 106. The valve body 116 has a fuel path. The valve seat 112 is attached to a downstream end of the valve body 116, and a fuel injection hole 112a is formed in the valve seat 112. The valve 110 is housed within the valve body 116, and can slide between an open position and a closed position. The valve comprises a shaft 109, an armature 108, and a ball 114. The armature 108 is attached to an upstream end of the shaft 109, and the ball 114 is attached to a downstream end of the shaft 109. The fuel injection hole 112a is open when the valve 110 is in the open position, and the fuel injection hole 112a is closed when the valve 110 is in the closed position. The spring 120 applies a biasing force on the valve 110, wherein the biasing force pushes the valve 110 in the closed position. The core 122 is disposed upstream from the armature 108. When the valve 110 is in the open position, an upstream end surface of the armature 108 makes contact with a downstream end surface of the core 122. When the valve 110 is in the closed position, the upstream end surface of the armature 108 is separated from the downstream end surface of the core 122. A non-magnetic ring 104 is disposed at an outer circumference side of the armature 108 and the core 122. The non-magnetic ring 104 extends from an upstream side of the armature 108 to a downstream side of the core 122. A downstream end of the non-magnetic ring 104 is fixed to the valve body 116, and an upstream end of the non-magnetic ring 104 is fixed to the core 122. A resin bobbin 102 is formed at an outer circumference of the non-magnetic ring 104 and the core 122, and the solenoid coil 106 is wound around the bobbin 102. An upper body 118 is disposed at an outer side of the solenoid coil 106, and a downstream end of this upper body 118 is connected with the valve body 116. An upstream end of the upper body 118 is connected with the core 122.
Pressurized fuel is supplied to the fuel injector 100 from fuel supply line (not shown). When the solenoid coil 106 is excited, a magnetic path is formed from the upper body 118, the valve body 116, the armature 108, and the core 122. At this juncture, the non-magnetic ring 104 prevents magnetic flux from short-circuiting from the valve body 116 to the core 122. When the magnetic path has been formed, the armature 108 is attracted by magnetic force, and the valve 110 retreats towards the core 122 side (towards a posterior end side) in resistance to biasing force of the spring 120. The fuel is thus injected from the fuel injection hole 112a. When the excitement of the solenoid coil 106 is halted, the biasing force of the spring 120 causes the valve 110 to advance towards the valve seat 112, and the injection of fuel is suspended.